It is well-known in the oil industry in the method of controlling downhole devices to use pressurised hydraulic fluid in a small diameter control line. The pressurised hydraulic fluid extends from a surface pump through the wellhead and connects to a downhole device such as a flow control valve(s). In the completion stage of well production it is generally required at some stage in the process that a production tubing string is closed off for testing. This allows, among other operations, for production packers to be set and tested.
Although a variety of processes and apparatus exist in the market for controlling valves, these prior art processes and apparatus are known to suffer from a number of disadvantages. For example, prior art processes and apparatus are known to be depth-dependent and therefore either their efficiency is reduced as depth is increased or they fail to work at depths commonly used in oil recovery. This can have a serious effect on the efficiency of oil production.
Generally, flow control valves are deployed as part of a tubing string with hydraulic control lines linked to the surface for remote activation. Remote activation of conventional double actuating flow control valves generally utilises two control lines, where one control line is used to open the valve and one control line is used to close the valve. Four control lines would be needed if two flow control valves were to be operated. In each case, one control line acts as the operational control line whereby fluid pressure is applied to the valve to cause the valve to open or close and the second control line for each operation of the valve acts as a return line. A double actuating control valve may be capable of being fully open to allow maximum flow through the valve, thereby maximising production or injection rates through the production string. This may also allow for easy access to the well and any equipment below the valve. In a fully closed position the valve is operable to close the flow path through the production string to allow testing of the tubing string to be carried out and to allow setting and testing of production packers etc.
Using a large number of hydraulic control lines leads to a complex apparatus which can easily break down. This is a major problem as this type of equipment is intended to be used in downhole completion operations hundreds of meters below the ground or sea-bed. Moreover, using a large number of hydraulic control lines increases the expense of the apparatus for potential users and increases the level of servicing required.
It is an object of at least one aspect of the present invention to obviate or mitigate at least one or more of the aforementioned problems.
It is a further object of at least one aspect of the present invention to provide an improved apparatus for controlling downhole flow control devices.
It is a further object of at least one aspect of the present invention to provide an improved method for controlling downhole flow control devices.